Plasma Chemistry Research Articles

Tantalum oxide and nitride spectral features from a laser-produced plasma

We report measurements of time-resolved Ta, TaO and TaN emission spectroscopic signatures from a laser-produced plasma. Plasmas were generated using 1064 nm, 6 ns pulses from an Nd:YAG laser focused onto a pure Ta metal target in a gaseous environment with varying percentages of O2/N2 for controlling gas-phase oxidation/plasma chemistry. Time-resolved analysis showed that Ta oxide emission is prominent at later times in plasma evolution, whereas strong atomic emission is present at early times in air. Emission spectral features as a function of O2 partial pressure showed that TaO emission intensity increases, while the peak intensity of TaO appears earlier with increasing O2 availability. We also report emission spectra of TaN, and show that plasma chemistry favors TaO formation instead of TaN when O2 is present in the environment.

Plasma chemistry and hematology reference values in wild nestlings of White-tailed Sea Eagles (Haliaeetus albicilla): effects of age, sex and hatching date

Studies on normal concentration of blood constituents of free-living birds are not very common. An adequate knowledge of blood chemistry is greatly recommended for those projects involving research and management of populations as far as they can be valuable for the assessment of the nutritional levels and health status of species. No previous published reports on these parameters from this species are available. The aim of this study was to obtain representative reference measures for hematologic and biochemical values in free-living clinically healthy wild White-tailed Sea Eagle nestlings (Haliaeetus albicilla). In addition, we investigated potential relationships between blood parameters, sex, age and hatching dates. Blood samples were obtained as part of routine monitoring and management when wild chicks were removed from their nest as part of a reintroduction program prerelease health check. A total of 83 nestlings, 43 males and 40 females, between 41 and 66 days of age (mean = 54.22, SD = 5.7), were sampled. Significant differences between sexes were found. Among hematological parameters, MCH, lymphocytes P and thrombocytes showed significant differences between males and females. In biochemical parameters, significant differences were found only in calcium, CK and LDH between sexes. No effect was found of age of the nestling when the sample was taken in any of the analyzed hematological parameters. No other significant relationships were found between biochemical parameters and other considered explanatory variables. Hatching date showed no relationship with blood parameters excepting urea. Urea was the only variable showing a strong relationship with hatching date, with those nestlings hatching later in the season showing higher urea concentration.

Effect of Mask Geometry Variation on Plasma Etching Profiles

It is becoming quite evident that, when it comes to the further scaling of advanced node transistors, increasing the flash memory storage capacity, and enabling the on-chip integration of multiple functionalities, "there's plenty of room at the top". The fabrication of vertical, three-dimensional features as enablers of these advanced technologies in semiconductor devices is commonly achieved using plasma etching. Of the available plasma chemistries, SF6/O2 is one of the most frequently applied. Therefore, having a predictive model for this process is indispensable in the design cycle of semiconductor devices. In this work, we implement a physical SF6/O2 plasma etching model which is based on Langmuir adsorption and is calibrated and validated to published equipment parameters. The model is implemented in a broadly applicable in-house process simulator ViennaPS, which includes Monte Carlo ray tracing and a level set-based surface description. We then use the model to study the impact of the mask geometry on the feature profile, when etching through circular and rectangular mask openings. The resulting dimensions of a cylindrical hole or trench can vary greatly due to variations in mask properties, such as its etch rate, taper angle, faceting, and thickness. The peak depth for both the etched cylindrical hole and trench occurs when the mask is tapered at about 0.5°, and this peak shifts towards higher angles in the case of high passivation effects during the etch. The minimum bowing occurs at the peak depth, and it increases with an increasing taper angle. For thin-mask faceting, it is observed that the maximum depth increases with an increasing taper angle, without a significant variation between thin masks. Bowing is observed to be at a maximum when the mask taper angle is between 15° and 20°. Finally, the mask etch rate variation, describing the etching of different mask materials, shows that, when a significant portion of the mask is etched away, there is a notable increase in vertical etching and a decrease in bowing. Ultimately, the implemented model and framework are useful for providing a guideline for mask design rules.

Understanding the temperatures of H3 + and H2 in diffuse interstellar sightlines

The triatomic hydrogen ion H 3 + is one of the most important species for the gas phase chemistry of the interstellar medium. Observations of H 3 + are used to constrain important physical and chemical parameters of interstellar environments. However, the temperatures inferred from the two lowest rotational states of H 3 + in diffuse lines of sight – typically the only ones observable – appear consistently lower than the temperatures derived from H 2 observations in the same sightlines. All previous attempts at modelling the temperatures of H 3 + in the diffuse interstellar medium failed to reproduce the observational results. Here we present new studies, comparing an independent master equation for H 3 + level populations to results from the Meudon PDR code for photon dominated regions. We show that the populations of the lowest rotational states of H 3 + are strongly affected by the formation reaction and that H 3 + ions experience incomplete thermalisation before their destruction by free electrons. Furthermore, we find that for quantitative analysis more than two levels of H 3 + have to be considered and that it is crucial to include radiative transitions as well as collisions with H2. Our models of typical diffuse interstellar sightlines show very good agreement with observational data, and thus they may finally resolve the perceived temperature difference attributed to these two fundamental species.

Unraveling Radical and Oxygenate Routes in the Oxidative Dehydrogenation of Propane over Boron Nitride.

Oxidative dehydrogenation of propane (ODHP) is an emerging technology to meet the global propylene demand with boron nitride (BN) catalysts likely to play a pivotal role. It is widely accepted that gas-phase chemistry plays a fundamental role in the BN-catalyzed ODHP. However, the mechanism remains elusive because short-lived intermediates are difficult to capture. We detect short-lived free radicals (CH3•, C3H5•) and reactive oxygenates, C2-4 ketenes and C2-3 enols, in ODHP over BN by operando synchrotron photoelectron photoion coincidence spectroscopy. In addition to a surface-catalyzed channel, we identify a gas-phase H-acceptor radical- and H-donor oxygenate-driven route, leading to olefin production. In this route, partially oxidized enols propagate into the gas phase, followed by dehydrogenation (and methylation) to form ketenes and finally yield olefins by decarbonylation. Quantum chemical calculations predict the >BO dangling site to be the source of free radicals in the process. More importantly, the easy desorption of oxygenates from the catalyst surface is key to prevent deep oxidation to CO2.

Electromagnetic enhanced ignition of octogen explosive at subnormal temperatures: A numerical study

The thermal decomposition and ignition of high-performance high explosives occur via a mechanism where the solid phase sublimes and the parent molecules decompose rapidly in the gas phase to form unstable and charged intermediates. These intermediates continue to react and form the final products to release energy and do work. We have observed that the presence of electromagnetic energy significantly reduces the ignition temperature of a common high explosive, and data suggest that this occurs via electromagnetic interactions with the charged gas-phase intermediates. Here, we modified the thermal decomposition kinetic expressions for octogen (High Melt eXplosive, HMX) to couple the effects of an incident microwave (MW) field. This modified kinetic model is used to investigate our previous experimental work which showed that the surface temperature at ignition of HMX powder is reduced by the MW field. The Fridman–Macheret α-model is a common approach in plasma chemistry and was incorporated into the Henson/Smilowitz HMX kinetics; this effectively reduces the activation energy (Ea) by vibronically excited charged reactive intermediates. A modified kinetic model was implemented into the COMSOL Multiphysics Software. The thermal time to ignition was validated; as a result, plasma formation reduced the surface temperature by ∼23 °C compared to thermal ignition. With a validated kinetic model that can simulate both pure thermal ignition and mixed thermal/plasma ignition, we are able to simulate our previous experimental work showing that plasma ignition reduces the surface temperature at ignition compared to thermal initiation.

Cold Atmospheric plasma treatments trigger changes in sun-dried tomatoes mycobiota by modifying the spore surface structure and hydrophobicity

The contamination of sun-dried tomatoes during processing can have a decisive impact on the quality of the finished product. In this study we investigated how Cold Atmospheric Plasma (CAP) under high surface power density (SPD) values can reduce fungal contamination in sun-dried tomatoes. In the application of this innovative processing method, the established “regime” for air plasma chemistry was the transition regime or NOx regime. First, we isolated and identified the mycobiota present on the tomatoes surfaces by mean of the analysis of the ITS region. The analysis revealed 32 different species, with A. niger , A. tubingensis, A. chevalieri , A. flavus, and A. alternata being the most abundant. Then, to reduce the fungal population, CAP-NOx was applied for 5, 10, 20 and 30 min on the surface of dried tomatoes. After incubation for 10 days, we observed that the antifungal effect was species and dose-dependent. In vitro investigation on the most abundant species revealed that A. chevalieri PSJ144 was the most sensitive species (almost 90%) immediately after 5 min of CAP treatment. With the increase of the exposure time up to 30 min, a strong reduction (p ≤ 0.05) of spore germination of A. alternata PSJ77 and A. tubingensis PSJ100 was observed (98 and 92%, respectively). However, spores of A. niger PSJ38 and A. flavus PSJ30 showed the highest resistance to the treatment. Moreover, the reparameterized Weibull function allowed to obtain useful information about germination kinetics as a function of time of CAP-NOx treatment, revealing that the resistance of the spores was: A. chevalieri < A. alternata < A. tubingensis < A . flavus < A. niger . In situ analyses confirmed a significant effect on natural fungal contamination by CAP-NOx treatment (76.5% of reduction), likely due to cell membrane rupture and cell death caused by plasma radicals. In addition, Pearson correlation analysis showed that spore resistance was highly correlated (p = 0.98) with their hydrophobicity. In a nutshell, our results clearly indicate that CAP-NOx treatment is an effective technique to reduce fungal contamination in sun-dried tomatoes. Among non-thermal processing methods, CAP shows promising perspectives of application in the tomato industry, to mitigate the effects of energy price rises. • A. niger , A. tubingensis, were most abundant species in dried tomatoes. • CAP reduced the fungal contamination on the dried tomatoes by 76.5%. • A. niger and A. flavus spores were more resistant ones to CAP. • A. chevalieri spores were inactivated after 0.1 min of CAP-NOx. • Spore hydrophobicity was correlated with the spore resistant to CAP.

Flexible Cold Atmospheric Plasma Jet Sources

The properties of non-thermal atmospheric pressure plasma jets (APPJs) make them suitable for industrial and biomedical applications. They show many advantages when it comes to local and precise surface treatments, and there is interest in upgrading their performance for irradiation on large areas and uneven surfaces. The generation of charged species (electrons and ions) and reactive species (radicals), together with emitted UV photons, enables a rich plasma chemistry that should be uniform on arbitrary sample profiles. Lateral gradients in plasma parameters from multi-jets should, therefore, be minimized and addressed by means of plasma monitoring techniques, such as electrical diagnostics and optical emission spectroscopy analysis (OES). This article briefly reviews the main strategies adopted to build morphing APPJ arrays and ultra-flexible and long tubes to project cold plasma jets. Basic aspects, such as inter-jet interactions and nozzle shape, have also been discussed, as well as potential applications in the fields of polymer processing and plasma medicine.

Two Rings Around One Ball: Stability and Charge Localization of [1 : 1] and [2 : 1] Complex Ions of [10]CPP and C60/70 [ *

We investigate the gas-phase chemistry of noncovalent complexes of [10]cycloparaphenylene ([10]CPP) with C60 and C70 by means of atmospheric pressure photoionization and electrospray ionization mass spectrometry. The literature-known [1 : 1] complexes, namely [10]CPP⊃C60 and [10]CPP⊃C70 , are observed as radical cations and anions. Their stability and charge distribution are studied using energy-resolved collision-induced dissociation (ER-CID). These measurements reveal that complexes with a C70 core exhibit a greater stability and, on the other hand, that the radical cations are more stable than the respective radical anions. Regarding the charge distribution, in anionic complexes charges are exclusively located on C60 or C70 , while the charges reside on [10]CPP in the case of cationic complexes. [2 : 1] complexes of the ([10]CPP2 ⊃C60/70 )+ ⋅/- ⋅ type are observed for the first time as isolated solitary gas-phase species. Here, C60 -based [2 : 1] complexes are less stable than the respective C70 analogues. By virtue of the high stability of cationic [1 : 1] complexes, [2 : 1] complexes show a strongly reduced stability of the radical cations. DFT analyses of the minimum geometries as well as molecular dynamics calculations support the experimental data. Furthermore, our novel gas-phase [2 : 1] complexes are also found in 1,2-dichlorobenzene. Insights into the thermodynamic parameters of the binding process as well as the species distribution are derived from isothermal titration calorimetry (ITC) measurements.

N2O5 in air discharge plasma: energy-efficient production, maintenance factors and sterilization effects

N2O5, a reactive species produced by air discharge plasma, has recently attracted much attention. Due to its high reactivity and solubility, N2O5 is a key molecule in nitrogen fixation processes and exhibits promising prospects in plasma biomedicine. However, thus far, it is not well known how to produce N2O5 efficiently and then maintain its concentration under the action of fast removal reactions. In view of this, N2O5 production by dielectric barrier discharge (DBD) alone and by the combination of DBD and gliding arc discharge is compared in this paper. It is found that the combination method can yield over three times the concentration of N2O5 compared to the single DBD method with the optimum discharge power. Moreover, the concentration of N2O5 in the effluent gas can be maintained once O3 also exists because O3 can continually produce N2O5 to compensate for its reduction. Finally, the sterilization effects of both the plasma effluent gas and plasma-activated water have trends similar to the trend of the gaseous N2O5 concentration, implying that N2O5 plays an important role in sterilization. This paper enhances the understanding of N2O5 chemistry in air discharge plasma and provides an effective way to produce and maintain N2O5 for subsequent applications.

The Deep Atmospheric Composition of Jupiter from Thermochemical Calculations Based on Galileo and Juno Data

The deep atmosphere of Jupiter is obscured beneath thick clouds. This causes direct observations to be difficult, and thermochemical equilibrium models fill in the observational gaps. This research uses Galileo and Juno data together with the Gibbs free energy minimization code GGchem to update the gas phase and condensation equilibrium chemistry of the deep atmosphere of Jupiter down to 1000 bars. Specifically, the Galileo data provides helium abundances and, with the incorporated Juno data, we use new enrichment values for oxygen, nitrogen, carbon and sulphur. The temperature profile in Jupiter’s deep atmosphere is obtained following recent interior model calculations that fit the gravitational harmonics measured by Juno. Following this approach, we produced pressure–mixing ratio plots for H, He, C, N, O, Na, Mg, Si, P, S and K that give a complete chemical model of all species occurring to abundances down to a 10−20 mixing ratio. The influence of the increased elemental abundances can be directly seen in the concentration of the dominant carriers for each element: the mixing ratio of NH3 increased by a factor of 1.55 as compared with the previous literature, N2 by 5.89, H2O by 1.78, CH4 by 2.82 and H2S by 2.69. We investigate the influence of water enrichment values observed by Juno on these models and find that no liquid water clouds form at the oxygen enrichment measured by Galileo, EH2O = 0.47, while they do form at higher water abundance as measured by Juno. We update the mixing ratios of important gas phase species, such as NH3, H2O, CO, CH4 and H2S, and find that new gas phase species, such as CN−, (NaCN)2, S2O and K+, and new condensates, namely H3PO4 (s), LiCl (s), KCl (s), NaCl (s), NaF (s), MgO (s), Fe (s) and MnS (s), form in the atmosphere.

Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde (CHD2CHO) and first detection towards IRAS 16293-2422

Context. The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined to be orders of magnitude higher than expected from the cosmic abundance of deuterium relative to hydrogen. The increasing number of singly and multi-deuterated species detections helps us to constrain the interplay between gas-phase and solid-state chemistry and to understand better deuterium fractionation in the early stages of star formation. Acetaldehyde is one of the most abundant complex organic molecules (COMs) in star-forming regions and its singly deuterated isotopologues have already been observed towards protostars. Aims. A spectroscopic catalogue for astrophysical purposes is built for doubly deuterated acetaldehyde (CHD2CHO) from measurements in the laboratory. With this accurate catalogue, we aim to search for and detect this species in the interstellar medium and retrieve its column density and abundance. Methods. Sub-millimetre wave transitions were measured for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered internal rotation of its asymmetrical CHD2 methyl group. An analysis of a dataset consisting of previously measured microwave transitions and of the newly measured ones was carried out with an effective Hamiltonian which accounts for the tunnelling of the asymmetrical methyl group. Results. A line position analysis was carried out, allowing us to reproduce 853 transition frequencies with a weighted root mean square standard deviation of 1.7, varying 40 spectroscopic constants. A spectroscopic catalogue for astrophysical purposes was built from the analysis results. Using this catalogue, we were able to detect, for the first time, CHD2CHO towards the low-mass proto-stellar system IRAS 16293-2422 utilising data from the ALMA Proto-stellar Interferometric Line Survey. Conclusions. The first detection of the CHD2CHO species allowed for the derivation of its column density with a value of 1.3×1015 cm−2 and an uncertainty of 10–20%. The resulting D2/D ratio of ~20% is found to be coincident with D2/D ratios derived for other COMs towards IRAS 16293-2422, pointing to a common formation environment with enhanced deuterium fractionation.

Determination of 915-MHz Atmospheric Pressure Air Microwave Plasma Torch (MPT) Parameters

The gas temperature, electron temperature, and electron density are critical parameters that affect microwave plasma chemistry processes in industrial applications. Using optical emission spectroscopy (OES), the gas temperature and electron density of a 915-MHz atmospheric pressure air microwave plasma torch (MPT) were investigated at various absorbed power levels and radial positions. In addition, the variation in the electron temperatures of 915-MHz atmospheric pressure argon microwave plasma filaments was analyzed as a function of the absorbed power. The experimental results showed that: 1) the absorbed power had little effect on the radial gas temperature or electron density; 2) the skin effect was present in the 915-MHz atmospheric pressure air MPT, where it causing caused hollowing in the center of the radial gas temperature distribution; 3) the electron density reached approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times10$ </tex-math></inline-formula> 13 cm−3 and was almost insensitive to variations in the absorbed power in the center of the 915-MHz atmospheric pressure air MPT; and 4) the upper limit of the 915-MHz atmospheric pressure microwave plasma filament electron temperature increased from approximately 1 to approximately 3 eV as the absorbed power increased from 2.0 to 6.3 kW.

Development of a practical soot model for diesel surrogate fuels and oxygenated fuels with specific soot precursor tracking and uniform model structure

Soot formation and oxidation involve several complex processes, which are driven by gas-phase chemistry and soot particle dynamics. An effective soot model for diesel surrogate and practical oxygenated fuels is necessary for predicting the soot emissions to meet the emission regulations in engines. To develop a practical and universal soot model for various fuels without tuning any model parameters under wide operating conditions, it is important to reproduce the soot behaviors for different fuels with distinct molecular structures. In this work, a practical soot model was developed to describe the soot behaviors for diesel surrogate fuels comprising large n-alkane, isoalkane, cycloparaffin, and aromatic hydrocarbon, as well as oxygenated fuels including alcohol and ether. The influence of the fuel molecular structures on the soot behaviors was emphasized by utilizing the specific reaction pathways of polycyclic aromatic hydrocarbon (PAH) production and the specific reaction channels of the soot formation including soot nucleation and PAH condensation for different fuels. An efficient method named the moment projection method (MPM) was employed to describe the soot particle dynamics by directly solving the moment transport equations and track the number of soot particles. By coupling a reduced chemical reaction model for describing the fuel oxidation chemistry and PAH formation, it is found that the soot volume fraction and number density are well predicted for iso-octane, n-heptane, toluene, methanol, n-butanol, dimethyl ether, their mixtures, and diesel surrogate in shock tubes and laminar premixed flames without tuning any model parameters. The effects of equivalence ratio, temperature, and fuel type on soot production are analyzed through the rates of soot nucleation, surface growth, PAH condensation, and oxidation. The computational results indicate that the present model can satisfactorily reproduce the soot characteristics of different fuels with distinct soot formation and oxidation processes.

Changing PM2.5 and related meteorology over India from 1950–2014: a new perspective from a chemistry-climate model ensemble

Surface PM2.5 concentrations in India have increased dramatically as emissions have risen in recent years. The role of meteorological factors in this increase is unclear, mainly due to a lack of long-term observations over the region. A 12-member ensemble of historical (1950–2014) simulations from the Community Earth System Model version 2-Whole Atmosphere Community Climate Model version 6 (CESM2-WACCM6) offers an unprecedented opportunity to examine simulated PM2.5 and meteorology for 20th century climates that can arise due to ‘climate noise’ under the same historical greenhouse gas and air pollutant emission trajectories. CESM2-WACCM6 includes interactive aerosol and gas-phase chemistry in the atmosphere coupled to ocean-sea ice-land models, and each ensemble member differs only in its initial conditions of the climate state. We systematically examine, decade-by-decade, the changes in PM2.5 and associated meteorology, including wind speed, surface temperature inversions, boundary layer height, precipitation, and relative humidity in four cities in India: Chennai, Kolkata, Mumbai, and New Delhi. Forced changes clearly emerge in meteorological variables from 1950 to 2014, including increases in both relative humidity and temperature inversion strength, and decreases in boundary layer height and average surface wind speed. The timing of these changes varies by city: boundary layer heights decrease most over New Delhi in the premonsoon season (ensemble average decrease of 400 m), but over Mumbai in the postmonsoon season (ensemble average decrease of 100 m). PM2.5 concentrations increase across India regardless of climate variability, with an almost threefold increase from 1950 to 2014 over New Delhi. Analysis of dimensionless variables shows that PM2.5 exhibits larger ensemble mean trends and smaller variability than the trends in the meteorological variables, enabling us to infer that the increase in PM2.5 is predominantly controlled by increases in anthropogenic emissions rather than climate variability. Overall, our simulations corroborate the dominant role of air pollutant emissions on poor air quality in India.

Prediction of the Propulsive Performance of an Atmosphere-Breathing Electric Propulsion System on Cathode-Less Plasma Thruster

Atmosphere-breathing electric propulsion (ABEP) is a type of electric propulsion system that uses the atmosphere as a propellant source instead of a stored reservoir. This technology is still in its early stages, but holds the promise of providing a clean, efficient, and sustainable propulsion system for spacecraft, enabling very low Earth orbit (VLEO) mission scenarios. To optimise the ABEP technology, accurately simulating air-based plasma chemistry plays a crucial role. In this paper, an air-based global model (GM) is presented that includes a detailed chemistry model for the various reactions that are involved in ABEP applications. The model’s goal is to forecast the performance of a cathode-less RF plasma thruster under various pressure levels and species concentrations that are typical of VLEO missions. The GM was exploited to map the performance of a fictitious ABEP based on a cathode-less RF thruster in order to assess its feasibility in VLEO. The numerical model is promising as a tool for the design of ABEP systems and for the preliminary optimization of mission scenarios.

Oscillations in gas-grain astrochemical kinetics

ABSTRACT We have studied gas-grain chemical models of interstellar clouds to search for non-linear dynamical evolution. A prescription is given for producing oscillatory solutions when a bistable solution exists in the gas-phase chemistry and we demonstrate the existence of limit cycle and relaxation oscillation solutions. As the autocatalytic chemical processes underlying these solutions are common to all models of interstellar chemistry, the occurrence of these solutions should be widespread. We briefly discuss the implications for interpreting molecular cloud composition with time-dependent models and some future directions for this approach.

A Modelling Study of Indoor Air Chemistry: The Surface Interactions of Ozone and Hydrogen Peroxide

Indoor surfaces play a key role in indoor chemistry, including modification of indoor oxidant concentrations. This study utilises the INdoor CHEmical Model in Python (INCHEM-Py) to investigate the impact of surface transformations and their impact on indoor gas-phase chemistry. INCHEM-Py has been developed to simulate the surface deposition of ozone and hydrogen peroxide onto nine and six individual surfaces respectively in a typical bedroom, kitchen and office for normal indoor concentrations in the absence of household activities. The results show that 91 to 96% of these oxidants are deposited onto indoor surfaces under our simulated conditions. In the bedroom, 38 to 44% of indoor ozone and hydrogen peroxide is deposited onto soft fabric surfaces, with 41 to 54% of ozone deposition occurring on plastic surfaces in the kitchen and office. Total indoor concentrations of straight-chained aldehydes (C1-C10) ranged from ≈ 4 to 5 ppb, with nonanal having the highest individual concentration (1.7, 1.6 and 1.5 ppb in the bedroom, kitchen and office respectively), primarily as a result of emissions from plastics following ozone deposition. Aldehyde concentrations following hydrogen peroxide deposition were often less than 0.01 ppb. Understanding how reactions and deposition on different indoor surfaces impact indoor air chemistry will enable internal surface selection with a view to improving overall indoor air quality.

Role of meteorology-driven regional transport on O3 pollution over the Chengdu Plain, southwestern China

Owing to the complex mesoscale meteorological dynamics, deep basin topography and pollutants emissions, the Chengdu Plain (CDP) situated at west border of the Sichuan Basin (SCB) have suffered excessive ozone (O3) pollution in the warm season. However, the meteorology-driven mechanism and associated dominant processes underlying the elevated O3 levels are not well elucidated due to limited ambient measurements. Here, we adopted trace gases data measured by basin-wide network in combination with a high-resolution chemical transport model for characterizing a regional continuous O3 episode occurred from 10 to 18 August 2019. The extensive monitoring network shapes a much-detailed evolution map of O3 concentrations which depicts that O3 hotspots extend from metropolitan areas to suburban areas across the CDP. It is found that both advection of O3-rich air masses in the residual layer (RL) and regional transport of O3 and its precursors under prevailing winds exert profound influences on the elevation of ambient O3 across the CDP. As the convective boundary layer is destroyed after sunrise, vertical mixing effects cause the entrainment of O3-rich air masses in RL to the surface, affecting the redistribution of surface O3 concentration. In addition, process analysis (PA) and integrated source apportionment method (ISAM) results of the CMAQ model indicated that vertical transport and gas-phase chemistry were the main sources of O3 during the day, while dry deposition and horizontal advection were the main sinks of surface O3. O3 transport by boundary condition (BCO) was the largest contributor to all urban O3 concentrations in the CDP. Our findings highlight the regional transport mechanism of O3 in SCB under complex topographic conditions and point out the physical and chemical causes and sources of typical summer O3 pollution episodes in the SCB.

2D simulations of inductive RF heating in the drivers of the SPIDER device

This paper presents the basic physical and numerical principles of a fluid model of the negative ions source. The model gives self-consistent two-dimensional description of the source, including the neutral gas flow, plasma chemistry, RF coupling in the source driver and plasma transport through the magnetic filter. The different particle species (electrons, the three types of the positive ions: H+, H2+, H3+, negative ions H− and the neutral species: hydrogen atoms H and molecules H2) are described by separate continuity equations and the electron temperature is governed by the electron energy balance equation. The particle fluxes are found from momentum equations neglecting the inertia terms (drift-diffusion approximation). The electrostatic coupling between electrons and ions is described by the Poisson equation. The paper focuses on details of the RF model and on the initial code developments to simulate the currents in the source induced by the RF currents flowing in the feeding coils. In our approach, the RF electrical field is split in a plasma part plus another one in vacuum, E = Ep + EV, which simplifies the boundary conditions for Ep while EV is obtained from a theoretical formulation for the field generated by a current loop, which results in a fast and flexible numerical algorithm providing converged solution for the RF field after a few iterations, even for the cases with high conductivity of the plasma. The numerical method is based on finite volume approximation and 9-point discretization is used to account on anisotropy due to magnetic field. The semi implicit numerical solver allows for large time steps (>1000× explicit time step) producing steady-state solution in a reasonable time (few hours for a typical mesh). The RF model has been successfully coupled to the fluid equations of the source and self-consistent solutions are analyzed in order to see the influence of the driver parameters and RF model assumptions (e.g. stochastic conductivity, induced magnetic field) on the heating efficiency and the plasma dynamics. It has been found that without magnetic field the plasma dynamics in the SPIDER source is almost independent on the details of the RF coupling model.